It is desirable in applications such as, for example, fuel control for automotive engines, to accurately measure the mass flow rate of a stream of air. Mass flow measurement is a critical component in a majority of residential, commercial, and industrial applications. Proper flow measurement can ensure balance, energy efficiency, and cost effectiveness. A thermal anemometer can be utilized to measure mass flow and temperature of the sensed media.
The majority of prior art thermal anemometers include the use of a mass flow sense element mounted to a ceramic substrate and containing a thick film and/or thin film bridge structure with discrete signal conditioning circuitry. The discrete signal conditioning circuitry can be utilized to convert sensed flow into a proportional analog output signal. The mass flow sense element and the signal conditioning circuitry can be connected utilizing wire bonds and wires on a printed circuit board (PCB) or ceramic substrate. Typically, such wire bonds and wires possess a further tendency to interact with the sensed media and form ionic contamination that can lead to false electrical signals or eventual failure. Additionally, wirebonds can increase undesirable turbulence and shift flow response. The wire is also susceptible to damage in a high mass flux environment, such as liquid flow, due to its thinness and upon attempts to clean the sensor. Unfortunately, such thermal anemometers are susceptible to damage caused by repeated or long term exposure of wire bonds and wires to external environments such as, for example, moisture, chemicals etc.
Based on the foregoing, it is believed that a need exists for an improved thermal anemometer flow sensor apparatus with a seal with a conductive interconnect for electrically connecting the sense die bridge (thin film or thick film) to the signal conditioning circuitry and providing a seal to isolate the bridge physically from external environment, as described in greater detail herein. The design of such a structure can enable mass flow sensing over wide ranges at a reasonable cost and provide trouble free operation in heretofore-hostile environments.